Scag won't start

I have a Cougar that is acting up. It has the 25 hp Kohler. It was starting ok and runs well when it starts, until you want to get off, I shut off the blades, then I engage the brake lever. This then makes the engine shut off and it will not restart. I have jumped all tha saftey switches with no relief, the starter has been checked out, and the battery is good. Is it possibly the starter switch? Any ideas would be appreciated!

I found the problem. It turned out to be the interlock relay. It would operate normally until it got hot. I changed it yesterday 8-31 and had no problems all day. Thanks to all who responded with ideas.